Transplacental transmission of hepatitis B virus

Establishment and characterization of a spontaneously immortalized trophoblast cell line (HPT-8) and its hepatitis B virus-expressing clone

BACKGROUND

Most trophoblast cell lines currently available to study vertical transmission of hepatitis B virus (HBV) are immortalized by viral transformation. Our goal was to establish and characterize a spontaneously immortalized human first-trimester trophoblast cell line and its HBV-expressing clone.

METHODS

Chorionic villi of Asian human first-trimester placentae were digested with trypsin and collagenase I to obtain the primary trophoblast cell culture. A spontaneously immortalized trophoblast cell line (HPT-8) was analyzed by scanning and transmission electron microscopy, cell cycle analysis, immunohistochemistry and immunofluorescence. HPT-8 cells were stably transfected with the adr subtype of HBV (HPT-8-HBV) and characterized by PCR and enzyme-linked immunosorbent assay.

RESULTS

We obtained a clonal derivative of a spontaneously immortalized primary cell clone (HPT-8). HPT-8 cells were epithelioid and polygonal, and formed multinucleate, giant cells. They exhibited microvilli, distinct desmosomes between adjacent cells, abundant endoplasm, lipid inclusions and glycogen granules, which are all characteristic of cytotrophoblasts. HPT-8 cells expressed cytokeratin 7, cytokeratin 18, vimentin, cluster of differentiation antigen 9, epidermal growth factor receptor, stromal cell-derived factor 1 and placental alkaline phosphatase. They secreted prolactin, estradiol, progesterone and hCG, and were positive for HLA-G, a marker of extravillous trophoblasts. HPT-8-HBV cells were positive for HBV relaxed-circular, covalently closed circular DNA and pre-S sequence. HPT-8-HBV cells also produced and secreted HBV surface antigen and HBV e antigen.

CONCLUSIONS

We established a trophoblast cell line, HPT-8 and its HBV-expressing clone which could be valuable in exploring the mechanism of HBV viral integration in human trophoblasts during intrauterine infection.

Quantitative analysis of HBV DNA level and HBeAg titer in hepatitis B surface antigen positive mothers and their babies: HBeAg passage through the placenta and the rate of decay in babies

It is well documented that perinatal transmission is the major cause of chronic HBV infection in China. However, the mechanisms of HBV perinatal transmission are not defined clearly. It is not known whether hepatitis B e antigen can cross the human placenta, and the rate of HBeAg decay in babies with and without HBV breakthrough has not been studied. In this study, HBV serological markers were investigated in 95 hepatitis B surface antigen positive pregnant women. These markers were also studied in the babies at birth and at the age of 6 months and 12 months. The data show that 7.4% (7/95) children were infected with HBV during the first year after birth despite receiving passive-active immunoprophylaxis with hepatitis B immune globulin and hepatitis B vaccine. The surface gene fragment of HBV DNA was cloned and sequenced following PCR amplification in 7 cases of HBsAg positive babies and their mothers. All babies had the same sequences as their mothers, although two babies also had sequences that would produce an amino acid substitution within the "a" determinant. Furthermore, we measured HBeAg titers and HBV DNA levels by using Abbott AxSYM system and LightCycler-based real-time fluorescence quantitative PCR in 54 mother-infant pairs. Thirty-three mothers were HBeAg positive, and 21 mothers were HBeAg negative. Seventy percent (23/33) of neonates from HBeAg-positive mothers were HBeAg positive at birth compared with 0% (0/21) of neonates from HBeAg negative mothers. HBeAg was present at higher titer in the birth sera of the babies with HBV breakthrough than in babies without breakthrough. HBeAg was cleared from the serum in all 19 babies without breakthrough. In 17 of these 19 babies, the HBeAg was cleared within 6 months, and in two babies clearance took 12 months. The mean serum HBV DNA level in the mothers of the 4 infants with HBV breakthrough was significantly higher than in the mothers of babies who did not become infected. In conclusion, this data suggests that HBeAg can cross the human placenta, and disappears from serum within 6 months in most babies. HBV DNA levels in hepatitis B carrier mothers are associated with the failure of HBIG and vaccine immunization, and the additional influence of transmitted HBeAg cannot be excluded.

Role of placental tissues in the intrauterine transmission of hepatitis B virus

OBJECTIVE

The purpose of this study was to determine the mechanism of intrauterine transmission of hepatitis B virus.

STUDY DESIGN

Placental tissues from 158 pregnant women who tested positive for hepatitis B surface antigen were examined for hepatitis B virus markers, Fc gamma receptors, and hepatitis B surface antigen-anti-hepatitis B surface antigen in different layers of cells.

RESULTS

It was shown that the hepatitis B virus infection rate among different layers of placental cells gradually decreased from the maternal side to the fetal side. Furthermore, the closer the infected cell layer was to the fetal side, the higher the risk of intrauterine hepatitis B virus infection. Fc gamma receptors were found on cells of both hepatitis B surface antigen positive and negative placentas; Fc gamma receptors III were found on trophoblastic cells and villous mesenchymal cells, and Fc gamma receptors II were found on only villous mesenchymal cells. Hepatitis B surface antigen-antibodies to hepatitis B surface antigen was detected in the cytoplasm and on the membrane of trophoblastic cells and villous mesenchymal cells in 2 hepatitis B surface antigen-positive placentas.

CONCLUSION

The results support the hypothesis that intrauterine hepatitis B virus transmission could be caused through "cellular transfer" in the placenta. One of the means of cellular transfer could be through Fc gamma receptor III-mediated entry of hepatitis B surface antigen-antibodies to hepatitis B surface antigen into cells.

Impact of hepatitis B immunisation as part of the EPI

Since 1992, hepatitis B vaccine has been an integrated part of Thailand's expanded programme on immunisation (EPI). Based on the data from five representative provinces, we have evaluated its impact on the countrywide prevalence of HBV infection and carrier rate. The population studied comprised 400-488 healthy and immuno-competent, subjects per area. The subjects' ages ranged from 6 months to 18 years. We examined their sera for viral hepatitis markers using commercially available test kits and established the coverage rate of hepatitis B vaccination after its inclusion into the EPI to be 71.2-94.3%. The number of individuals undergoing the complete course of vaccinations had increased four-fold. Consequently, only 0.7% of the children born after the implementation of this the novel EPI strategy were HBV carriers.

Persistence of antibodies to the surface antigen of the hepatitis B virus (anti-HBs) in children subjected to the Expanded Programme on Immunization (EPI), including hepatitis-B vaccine, in Thailand

Will hepatitis-B vaccine administered at birth, and at 2 and 6 months of age, as an integral part of Thailand's Expanded Programme on Immunization, provide long-term protection? In an attempt to answer this question, residents of five provinces (representing five distinct geographical areas of Thailand) who were aged 1-10 years and had received this course of vaccination were enrolled on a serological study. Each was tested, with ELISA, for the surface antigen of hepatitis B (HBsAg) and for antibodies against this antigen (anti-HBs) or against the core antigen (anti-HBc). Over all age-groups, the prevalences of HBsAg, anti-HBs and anti-HBc were 0.67%, 71.4% and 5.5%, respectively. Although the prevalence of anti-HBs decreased with age, it remained at 56%-65% among those aged 6-10 years. Between 2% and 17% of the subjects aged 1-9 years had high titres of anti-HBs. Based on these results, an additional booster, still a controversial issue, does not appear to be required in order to prevent infection with hepatitis B virus and thus permit the eventual eradication of chronic carriage and its fatal sequelae in Thailand.

H-2(d) mice born to and reared by HBeAg-transgenic mothers do not develop T cell tolerance toward the hepatitis B virus core gene products

The function of the secretory core gene product (HBeAg) of the human hepatitis B virus (HBV) is unknown. It has been proposed that this protein may be passed from the mother to her offspring at the perinatal stage where it might induce immune tolerance. In a previous study we have shown that the murine placenta presents an efficient barrier for the HBe protein and that H-2(b) mice born to HBeAg-positive transgenic mothers do not develop tolerance of specific cytotoxic T cells. In the present work we demonstrate that transgenic mice expressing high serum levels of HBeAg secrete only small amounts of this protein into their milk and excrete minute amounts of the viral gene product in their urine. Furthermore, it is shown that nontransgenic H-2(d) mice born to and reared by HBeAg-positive mothers exhibit a reactivity of HBc/eAg-specific CD4(+) Th cells and CD8(+) cytotoxic T cells comparable to that of normal isogenic control mice. In accordance with this observation the humoral immune responses directed against the HBeAg were comparable between these two groups of animals. This finding indicates that H-2(d) mice potentially exposed to small amounts of maternal HBeAg transferred by the transplacental, lactogenic, or renal route do not develop tolerance toward the HBV core gene products. These data challenge the hypothesis that a potential function of the HBeAg may be to operate as a tolerogen at the perinatal developmental stage.

Molecular analysis of the a determinant of HBsAg in children of HBeAg-positive mothers upon failure of postexposure prophylaxis

OBJECTIVE

To investigate the a determinant of hepatitis B virus (HBV) S gene for the presence of mutations responsible for vaccine failure.

METHODS

The a determinant of HBV S gene was amplified in sera obtained from 11 HBV-positive infants and children born to asymptomatic HBeAg-positive mothers by nested polymerase chain reaction (PCR) and subsequently subjected to direct sequencing. The sequences obtained were translated into the corresponding amino acids and compared to amino acid sequences of HBV subtype adr. All infants under investigation had received recombinant hepatitis B vaccine within 24 hours after delivery and had completed the recommended vaccination course, consisting of three to four doses administered at defined intervals.

RESULTS

The usual divergence regarding genotype and subtype was identified among the 11 samples tested. Only two exhibited a point mutation within the a determinant, one of which consisted of a substitution of glycine with alanine at position 145, and the other of a substitution of glutamine with arginine at position 129.

CONCLUSION

Eleven neonates were positive for HBV infection, and two of them showed point mutations that might have rendered the virus resistant to the vaccine, possibly due to a change in the S protein's secondary structure. Yet, this remains a matter of speculation, since the other seven cases positive for hepatitis B viral DNA merely demonstrated the usual genotype and subtype. The presence of escape mutants of HBV can be considered rather negligible with respect to vaccination programs, especially as the vaccine has been shown to reduce hepatitis B, as well as hepatocellular carcinoma efficiently.

The hepatitis B virus e antigen cannot pass the murine placenta efficiently and does not induce CTL immune tolerance in H-2b mice in utero

The function of the secretory core gene product (HBeAg) of the human hepatitis B virus is unclear. It has been discussed that this protein may be passed from the mother to the fetus, where it might induce immunologic tolerance. Here we have examined this possibility with transgenic mice expressing high levels of HBeAg. Analysis of serum samples obtained from nontransgenic fetuses which developed in HBeAg-positive mothers showed no evidence that the HBeAg can pass the placenta. Moreover, direct examination of the HBeAg- and HBcAg-specific cytotoxic T-cell immune response of H-2b mice which developed in either transgenic or nontransgenic mothers revealed no indication that mice which could have been exposed to the HBeAg in utero become tolerant to HBV core gene products. From these data we conclude that the placenta represents an efficient barrier for HBeAg transfer and that the HBeAg does not tolerize cytotoxic T cells, at least in mice of the H-2b haplotype.

Mutations in the 'a' determinant of hepatitis B surface antigen among Chinese infants receiving active postexposure hepatitis B immunization

Twenty-four infants who became positive to the surface antigen of hepatitis B virus (HBsAg) despite a complete course of active postexposure immunization with plasma derived hepatitis B vaccine were studied. The polymerase chain reaction amplified products of the common neutralizing epitope 'a' determinant of HBsAg (Nucleotide 419-598) from serum samples were sequenced and analyzed for nucleotide mutations. Four cases (16.7%) had mutations that led to amino acid substitutions between codons 124 and 147. Only one case (N1) showed a substitution at codon 145 (from glycine to arginine, 145R), the other three were at codons 126-129. The mother of N1 was co-infected with the wild type and the mutant virus. Five years later, serum of N1 showed only the wild type virus. There was no significant relationship between the mutation rate and the anti-HBs response to hepatitis B vaccination. Results suggest that without immune selective pressure, 145R variant was not frequently observed, and was not stable. Mutation in the 'a' determinant was not an important cause of failure to prevent maternal-infant transmission of HBV by active postexposure hepatitis B immunization in Chinese children.

Early invasive prenatal diagnosis in HBsAg-positive women

From 1982 to 1989, pregnant women in two large city hospitals in The Netherlands had serum samples screened for hepatitis B surface antigen (HBsAg). Infants of mothers found to be HBsAg-positive received hepatitis B immune globulin immediately after birth and hepatitis B vaccine in the first year of life. Blood samples of infants were regularly tested for HBsAg and antibodies directed against HBsAg. A retrospective analysis of the pregnancy outcome in HBsAg-positive women who had invasive tests for prenatal diagnosis was carried out to determine whether amniocentesis and chorionic villus sampling (CVS) are risk factors for the intrauterine transmission of the hepatitis B virus. Amniocentesis was carried out in 17 HBsAg-positive women and CVS in one case. Only two women were HBsAg- and HBeAg-positive. Prenatal diagnosis led to the termination of pregnancy for fetal chromosome abnormality in three cases. The remaining 15 pregnancies were uneventful; all infants were negative for HBsAg and developed an active immune response to the vaccine. These data suggest that amniocentesis in HBsAg-positive women constitutes a low risk for the intrauterine transmission of the hepatitis B virus, but definite conclusions in HBeAg-positive women cannot be drawn.

Is a function of the secreted hepatitis B e antigen to induce immunologic tolerance in utero?

Infants born to hepatitis B virus carrier mothers, who express a secreted form of the nucleocapsid antigen designated HBeAg, invariably become persistently infected. To investigate the role of immunologic tolerance mechanisms in chronic infection of the newborn, we have generated HBeAg-expressing transgenic mice. HBeAg-expressing transgenic mice were tolerant to both HBeAg and the nonsecreted nucleocapsid (hepatitis B cor antigen/HBcAg) at the T-cell level. Transgenic mice did not produce antibody to HBeAg but did produce anti-HBc antibody in vivo and in vitro. The coexistence of tolerance to HBc/HBe T-cell determinants and anti-HBc antibody production in vivo parallels the immunologic status of neonates born to carrier mothers. It was also demonstrated that the maintenance of T-cell tolerance to HBcAg/HBeAg required the continued presence of the tolerogen and in its absence persisted for less than 16 weeks. The reversibility of T-cell tolerance to HBcAg/HBeAg may explain the inverse correlation between age of infection and rates of viral persistence. These observations suggest that a function of the HBeAg may be to induce immunologic tolerance in utero. Expression of HBeAg may represent a viral strategy to guarantee persistence after perinatal infection.

Hepatitis B virus infection in children

Several modes of transmission can account for the high hepatitis B virus (HBV) carrier rate observed in children and young adults; perinatal transmission, horizontal transmission from household members and playmates, transmission due to sexual contact with a carrier. An inverse correlation has been reported between the age at which HBV infection occurs and the development of the carrier state. The epidemiology of HBV infection in children has important implications on strategies for prevention and control of this disease.

Hepatitis B vaccine in the prevention of perinatally transmitted hepatitis B virus infection: final report on a West Midlands pilot study

A four-dose vaccination schedule was used to interrupt perinatal transmission of hepatitis B virus from carrier mothers to their babies. Of 49 babies immunised and successfully followed up, 43 (88%) became immune: 15 out of 21 (71%) of babies born to HBeAg + mothers became immune, the other 6 becoming the only carrier babies in the study. Without immunisation a carrier rate in excess of 70% would have been expected in this high-risk group. Vaccine alone, given in a rapid immunisation schedule, protected the majority of babies at risk. In those babies in whom the carrier state occurred in spite of immunisation, infection may have taken place in utero, or the infant may have failed to produce adequate antibody in response to the vaccine.

Significance of maternal and infant serum antibodies to hepatitis B core antigen in hepatitis B virus infection of infancy

The significance of IgM and IgG class antibodies to hepatitis B virus (HBV) core component (anti-HBc) was investigated in a study of maternal-fetal HBV transmission. An IgM anti-HBc response was lacking in the majority (49/53) of HBV-infected infants. This antibody thus cannot be used as an indicator of transplacental infection. However, most infants who became HBsAg positive during the first 6 months of life acquire infection in the perinatal period rather than transplacentally. Passively transferred maternal IgG anti-HBc in the infant and additional IgM anti-HBc positively in the carrier mother have no modulating influence on HBV infection of infants born to HBV carrier women.

Transplacental leakage of HBeAg-positive maternal blood as the most likely route in causing intrauterine infection with hepatitis B virus

Thirty-two HBeAg-positive carrier mothers and their 32 babies were investigated to elucidate the mechanism involved in intrauterine infection with HBV. Five mothers had symptoms and signs of threatened abortion and/or threatened preterm labor. Three mothers gave birth more than 6 weeks after the episodes, and their babies were those infected in utero. The other two gave birth within 1 week after the episodes, and the two babies were treated with HBIG immediately after birth; HBV infection was successfully prevented. Therefore we suggest that transplacental leakage of HBeAg-positive maternal blood, which is induced by uterine contractions during pregnancy and the disruption of placental barriers, is the most likely route to cause HBV intrauterine infection.

Anti-HBc screening for the prevention of perinatal transmission of hepatitis B virus in France

As anti-HBc screening has been proposed for blood donor testing, we investigated its effectiveness during pregnancy. Among 4,023 successive pregnant women screened for anti-HBc, 539 (13.4%) were positive and further tested for HBsAg and anti-HBs. HBsAg was found in 73 (1.81%) and anti-HBc only was positive in 66 (1.64%). Among the 73 women positive for HBsAg, HBV DNA was found in the serum of seven, the cord blood of two, the placenta of three. Of the 58 infants given HBV immunoglobulins and vaccine, only four had transient HBsAg. None of the 66 women positive for anti-HBc only had anti-HBc IgM, HBeAg, or HBV DNA in serum, cord blood or placenta but five women became HBsAg positive before, at, or after delivery. Among the infants born of these 66 mothers, three had high ALT, two had HBsAg and one HBV DNA without HBsAg. Screening for anti-HBc may be cost effective, at least in low HBV prevalence areas, since there is evidence for infectivity of pregnant women positive for anti-HBc only.

Perinatal transmission of hepatitis B virus in high-incidence countries

Hepatitis B is a serious public health problem throughout the world. Hepatitis B virus (HBV) induces acute hepatitis with a case-fatality rate of about 1%. Even more important, 5-10% of patients infected with HBV become chronic carries and about 25% of these will die due to cirrhosis and hepatocellular carcinoma. The reservoir of HBV chronic carriers in the world is estimated at more than 200 million people and 80% of them reside in Asia and the western Pacific. In high-incidence areas, such as south-east Asia, perinatal transmission of HBV from carrier mothers to newborns appears to be the most important factor for the high prevalence of HBV infection and 70-90% of infants born to HBsAg/HBeAg-positive mothers become chronic carriers. Three possibilities of transmission of HBV from carrier mothers to newborns are suggested: (a) transplacental transmission in utero - it was estimated that such transmission occurred in 5-15% of newborns; (b) transmission during delivery, which is considered the main mode of perinatal transmission; (c) postnatal transmission from mother to newborn, which is not common. HBeAg is the main maternal factor in determining whether infection of newborns will occur; the expression of this antigen seems to be determined genetically. Recently it has shown that immunoprophylaxis is highly effective in preventing the development of the carrier state in infants born to HBsAg/HBeAg-positive mothers. Only 5-10% of high-risk infants are not protected by vaccination. If it becomes possible to immunize the entire world population including all babies born to carrier mothers at birth, and if our knowledge of the mechanisms of perinatal transmission of HBV is accurate, the carriers and acute cases of HB ought to disappear in two to three generations.